clarify the exhaustiveness check with TypeScript

docusaurus/src/functions/submitMathInputForm.ts

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: AGPL-3.0-or-later */
 
 import React from "react";
+import typescriptNever from "./typescriptNever";
 
 export default (event: React.FormEvent<HTMLFormElement>): void => {
   event.preventDefault();
@@ -15,8 +16,7 @@ export default (event: React.FormEvent<HTMLFormElement>): void => {
   } else if (i instanceof File) {
     console.warn({ i });
   } else {
-    const typescriptExhaustivenessCheck: never = i;
+    typescriptNever(i);
-    console.warn({ typescriptExhaustivenessCheck });
   }
 
   window.location.assign(url);